Damages of home electric appliances from lightning surges through a distribution line have recently increased. Installation of SPDs (Surge Protective Devices) in indoor distribution line is one of countermeasures against the damages. However, installation of SPDs is not prevalent because the effect of it is uncertain and it is expensive.
Therefore, to ascertain effects of the SPD, they were verified by means of experiments in various cases. As a result, an SPD in the switchboard wholly suppressed over-voltages in the indoor distribution line and an SPD installed near a home electric appliance did over-voltages in one indoor distribution branch line near the SPD. But the SPD for the appliance did not suppress over-voltages in the other indoor distribution branch lines. Installation of an SPD in the switchboard is one of effective methods to protect home electric appliances against lightning surges through a distribution line.